The invention relates to boilers such as large utility boilers that are disposed in a frame that is provided to withstand the internal furnace gas pressure. As the furnace approaches operating temperature, the furnace walls expand vertically and horizontally. Additionally, the pressure excursions within the furnace, either an increase or a decrease in pressure within the furnace, cause a resultant additional flexing of the tube walls either inwardly or outwardly in a horizontal direction.
It has become customary and necessary to provide an arrangement of flanged girder beams, typically referred to as buckstays, that extend around the furnace to provide additional support to the furnace wall and prevent the dishing of the furnace walls in a horizontal direction because of pressure variations. More particularly, the arrangement typically uses both vertical and horizontal structural members that are respectively known as vertical and horizontal buckstays.
Typically, the horizontal buckstays are disposed in bands around the perimeter of the furnace tube walls at vertically spaced intervals (often between 15 and 40 feet) throughout the height of the furnace wall. Horizontally, the buckstays on opposite walls of the furnace are interconnected through buckstay ties so that the reaction of one buckstay is resisted by the reactions of the buckstay on the opposing wall so it can counteract the pressure forces acting on the furnace walls. It has been customary to provide vertical support members to interconnect adjacent buckstays with a connection that permits a sliding action that permits relative movement between the furnace tube wall with which a buckstay cooperates and the buckstays themselves. As the furnace expands in a vertical direction the effect on the various levels of buckstays will be different. This will be apparent because the elongation of the furnace tube walls will be different at different points in the furnace. This relative vertical expansion between the furnace tube wall structure and the buckstays will produce a very high localized bending moment on the buckstays. It has been customary to relieve bending moments with these vertical support members which extend between neighboring buckstays. Arrangements for relieving or preventing the bending movement of this type are disclosed in U.S. Pat. Nos. 3,461,847 and 3,861,360.
The invention also relates to an attachment to such buckstays that will cause the vertical buckstay to also act as a leveler. A leveler is a device that will provide lateral stability for the horizontal buckstay as well as maintaining its level position.
In such buckstay arrangements utilizing vertically extending support members for linking the vertically adjacent buckstays and absorbing the bending moment, the structural system is necessarily massive and also somewhat rigid. Therefore, the structural support system has a certain amount of inertia which must be overcome before the structural system can flex properly in response to pressure changes within the furnace and thereby absorb the pressure forces acting on the furnace walls. In the event there is a sudden change in furnace pressure, and explosive or implosive load may be exerted on the furnace tube walls over a very short period of time. In such a system as described above wherein the band of buckstays are interconnected in a vertical direction, it has been observed that the buckstay system may in some instance be incapable of responding to such a sudden change in furnace pressure without permanent damage to the buckstay system and/or the furnace wall.
The prior art apparatus that attaches the vertical buckstay to the horizontal buckstay is overly complicated. More particularly, one current design uses a pin in a slot of one of the in connections. Loading in a vertical buckstay that can be transmittal to the horizontal buckstay is small because of the line contact between the pin and the slot.